1. Field of the Invention
This invention relates generally to the hydraulic shock absorber art and more particularly to an improved shock absorber which has the capability to automatically adjust for fluid viscosity variations as a function of temperature.
2. Prior Art
Prior art hydraulic shock absorbers generally include a pressure tube, a piston connected to a piston rod slidably mounted in the pressure tube, orifices in the pressure tube communicating to a reservoir, and metering means for adjusting the size of the orifices. During load deceleration, hydraulic fluid in the pressure tube is forced through the orifices into the reservoir as the piston is forced by the load into the pressure tube.
The prior art discloses that by designing the orifices to be either exponentially sized and equally spaced along the pressure tube, or exponentially spaced along the pressure tube but equally sized the shock absorber provides a uniform stopping force as well as a uniform deceleration to the load throughout the piston stroke. This feature is exemplified by U.S. Pat. Nos. 4,133,415; 4,059,175; 4,174,098; 3,446,317; and 3,207,270.
In addition, the prior art shock absorbers have some mechanism for adjusting the effective size of the orifices between the pressure tube and the reservoir to adjust for loads with varying velocities and masses. One mechanism for adjusting the orifice size has been to mount a sleeve over the pressure tube so that apertures in the sleeve combine with the apertures in the pressure tube to form orifices between the pressure tube and the reservoir. By rotating the sleeve, the orifice sizes are increased or decreased. This class of metering mechanism is exemplified by U.S. Pat. Nos. 4,133,415; 4,059,175; 4,174,098; 3,750,856; and 3,510,117.
Other prior art discloses additional metering means. U.S. Pat. No. 4,164,274 discloses a metering spool with lands to adjust the size of the orifices. By rotating the spool, the spool is moved axially, thereby causing the lands to more or less cover apertures in the pressure tube. U.S. Pat. No. 3,446,317 discloses two mechanisms for adjusting the orifice's sizes: a rotatable rod with flat or chordal grooves, and a rotatable tubular member having a plurality of orifices of different diameters. U.S. Pat. No. 3,207,270 discloses a flow control member in the form of a wedge member mounted for longitudinal adjustment relative to an inclined support member.
A disadvantage of all of the prior designs is that although the orifices can be adjusted manually for varying loads, the orifices are not automatically varied in size as a function of temperature to account for variations in fluid viscosity. Thus, the prior art shock absorbers are not always properly adjusted for their loads.
The present invention is a shock absorber of the general type described above; however, the present invention is provided with a unique orifice metering means that operates to automatically compensate for changes in fluid viscosity as a function of temperature by automatically adjusting the effective orifice sizes.
The present invention also is less complex in construction than prior art shock absorbers, which are costly to manufacture and have many parts. The prior art shock absorbers are also difficult to maintain and must be manufactured to extremely close tolerances to eliminate undesirable leakage.